In WO2008087593, an illumination device for illuminating a surface, comprising a lighting element and an illuminating body is described. The illuminating body can receive artificial light from the lighting element and deflect the received light onto the surface. The device may be placed with the illuminating body over a book or other surfaces for illuminated viewing through the transparent illuminating body. The advantage of the illumination device is that it can not only illuminate a flat surface, but also a curved surface, and that it minimizes the distortion of the images/texts on the curved surface.
However, after being powered on, the whole illuminating body, which normally is as large as a book or a magazine, is illuminated, while the user only focuses on a limited number of lines at any one moment. This decreases the illumination efficiency and reduces the time the illumination device can be operated without recharging or replacing the energy source(s). Therefore there is a need to improve the efficiency with which light is used in this kind of illumination devices.